'86 blackmax 150 hp: Loss of Power

[duhn]

I have always had problems with the motor ever since I bought the boat 2 years ago. My latest issue has been the motor would occasionally lose power after a long outing, 20 to 30 miles. I would have to throttle down to avoid stalling. Then it would get back on plane, then do it again. It seems like going up the backside of a swell causes this. As the day progresses it will not go faster than 5 knots. After many many posts and replies, I thought I had the problem solved. I replaced the coils and the plug wires. Friday night I took the boat out, ran like a champ. It got up to 31 knots, the fastest it has ever ran. got up on plane fast and throttle response was incredible. Seas were flat like a lake, no swells to climb. I thought I had the problem solved. Decided to take it out Saturday morning. Weather was up and seas were bumpy. 18 miles out.......LOSS OF POWER. Limped back home at 8 knots(3 hours). 1 mile before home, 5 knots max. Inside the breakwall 20 min idle to the launch ramp, I gave it one last try, and it reved up. Had to let up because I was in a no wake zone. I was able to run it up the trailer with plenty of power.

What gives? Is something getting warm and failing? Are the bumpy seas causing something to come loose? Did the 20 min ride inside the breakwall allow the problem to cool down? Can compression change with engine temp? The only thing I haven't changed is the stator, trigger and switch boxes. Are these symptoms of these failing?
BTW, I have been through the entire process.. fresh fuel, 100 psi compression each cylinder, fuel pump, primer bulb, Stator was checked.
Please help... It is lobster season and my honey hole is 29 miles away

 

[j_martin]

Re: '86 blackmax 150 hp: Loss of Power

Fuel tank vent.

 

[jake505]

Re: '86 blackmax 150 hp: Loss of Power

do you have permantly built in fuel tanks or the portable "red" tanks. have you checked the fuel filter or maybe there is something wrong with the pick up in your tank. you could always try taking a new portable tank and drive around with the reg tank hooked up and then when it starts lossing the power switch to the new one and see if the problem goes away. If your tank has a hose in side for the pick up it sounds like maybe it got a hole in it and when the fuel level goes down the engine could be sucking air and the wave to could be causing it when the fuel sloshs to one side of the tank or something like that. I would do start by checking out the tank for sure though.

 

[duhn]

Re: '86 blackmax 150 hp: Loss of Power

Fuel tank vent.

Are you talking about the one that the gas comes out of to let you know the tank is full?

 

[j_martin]

Re: '86 blackmax 150 hp: Loss of Power

Are you talking about the one that the gas comes out of to let you know the tank is full?

It sounds like when you get this problem put to bed, the next project is a fuel/air separator on your vent line. I gained about 4 gallons of usable capacity and got rid of a lot of pollution when I fitted mine.

What you are describing sounds like a fuel delivery issue. One I had like that turned out to be an oil bottle foil seal in the gas tank, occasionally plugging up the pickup screen. A pinhole leak in the pickup tube, which is not uncommon, will cause it to run a lot better on a full tank than a half full tank.Suction line air leaks anywhere could cause it.

At any rate, you need to get to the bottom of it because just before it flames out on you, it's leaning out, and sometimes 2 cycle motors eat pistons under those conditions.

If you put a short piece of clear tubing in your fuel line just before the bayonet to look for air bubbles. The bayonet fitting is suspect. If the fuel lines are old, you could have an inner tube in one collapsing.

hope it helps
John

 

[duhn]

Re: '86 blackmax 150 hp: Loss of Power

Fuel tank vent.

Hey John,
Fuel has never come out of the vent to let me know the tank is full. I got into it and discovered that it is indeed venting. I did notice that the hose to the vent has a loop in it (not a kink). Could that prevent it from venting properly with fuel sitting at the bottom of the loop? Kinda line a P-Trap in a sink. Is that loop supposed to be there? should I cut it shorter to eliminate the loop?


Devin

 

[j_martin]

Re: '86 blackmax 150 hp: Loss of Power

Hey John,
Fuel has never come out of the vent to let me know the tank is full. I got into it and discovered that it is indeed venting. I did notice that the hose to the vent has a loop in it (not a kink). Could that prevent it from venting properly with fuel sitting at the bottom of the loop? Kinda line a P-Trap in a sink. Is that loop supposed to be there? should I cut it shorter to eliminate the loop?


Devin

Yup
Nope
Yup

I would guess the loop is someones idea of a anti splash setup. It ain't good fer sure.

I put in a Racor LG50 fuel air separator. It solved the fuel splash problem very nicely, yet vents freely.

 

[duhn]

Re: '86 blackmax 150 hp: Loss of Power

Thanks John,
I'll give it a try this weekend. Hopefully I can rid this boat of the curse.

 

[sschefer]

Re: '86 blackmax 150 hp: Loss of Power

The problem you are describing does sound like fuel delivery and if it is, it's not all that uncommon.

Off Shore boats are sometimes equipped with a surge tank(s) to combat the ever changing attitude of the boat that causes sloshing in the tank and areation of today's oxygenated fuels.

They are also finding that many of the fuel/water separators in use today have a tendency to aerate fuel due to vibration. This is most common with 10 Micron filters. The Merc fuel water separator for pulse type fuel pumps is 25 Micron.

In automobiles they combat the situation by placing the fuel pump in the fuel tank. On boats with outboard motors and pulse style low pressure fuel pumps, solutions have been to place a 1-2 lb electric fuel pump before the fuel water separator. These small helper fuel pumps can be found at Kragen/Oriely's for around 45.00. They should (according to the instructions) be mounted below the tank and vertically however I found that they seem to work fine above the tank and horizontal which I think is safer.

To power the pump, the safest configuration is to add a second voltage regulator that is not connected to your battery and run the fuel pump from it via a relay. This will cause the fuel pump to not run unless the engine is running and you keep your primer bulb. On a 4 stroke you could use a oil pressure sensor which is a commonly accompanying solution with marine electric fuel pumps.

Converting from pulse to an electric fuel pump is another option where you would remove your pulse pump and use a Walbro Marine Grade lifting pump placed after the fuel/water separator and a pressure regulator adjusted to 5lbs max so you don't overpower your carb float needle valves. The Walbro pump can lift fuel up to about 2 feet which is adequate for most below deck tanks.

You can find Walbro pumps at http://www.walbro.com They are no more expensive than Aero's or Holley's. I've never tried it but you should be able to keep your oil injection by tee'ing in the check valve but I think the general concesous will be that it should be removed and you should mix your oil in the tank.

 

[duhn]

Re: '86 blackmax 150 hp: Loss of Power

Just got back from a test run. It didnt take long for the motor to lose power. Not even a half mile on plane. the seas were not bad at all. I switched to a spare tank....same problem. It is just so random.


I'm at a loss.

 

[j_martin]

Re: '86 blackmax 150 hp: Loss of Power

Just got back from a test run. It didnt take long for the motor to lose power. Not even a half mile on plane. the seas were not bad at all. I switched to a spare tank....same problem. It is just so random.


I'm at a loss.

To determine if it is fuel (which we all suspect) or electrical (we could be wrong) , install a 1/8" NPT to hose (whatever works out) adapter in the last, unused fuel fitting on the carb bank. It's probably the lowest port one. Rig a hose (vinyl hardware stuff will work for this) to where you can have a 10 - 15 lb gauge to read. You could buy one, or steal one off'n grandma's pressure kettle, It just has to read about 6 lbs fuel pressure.

Watch what it does when the engine dies. If it goes down to zero, it's a fuel problem. If it stays up while the engine is struggling, it's ignition.

Been there, done that.
John.

 

[duhn]

Re: '86 blackmax 150 hp: Loss of Power

Finally got a chance to set up a fuel pressure gauge. Pressure checked out ok when it bogged down.

When I got home I took apart all 3 carbs and started inspecting them closely. I noticed that the plastic float has an aluminum tab that the needle hooks on to. This piece of aluminum is loose. Basically when the fuel in the bowl is going down it lifts up on a needle and lets fuel in. With this being loose it doesn't open up far enough to let enough fuel in.

COULD THIS BE THE PROBLEM?

Is there a way to tighten this tab down? Its hard to explain, but this alum tab has plastic melted to hold it in place. I'm thinking that using a soldering iron to melt it down more should do the trick. Do you think it will blow up because it has been living in fuel for 20 something years?

 

[j_martin]

Re: '86 blackmax 150 hp: Loss of Power

Finally got a chance to set up a fuel pressure gauge. Pressure checked out ok when it bogged down.

When I got home I took apart all 3 carbs and started inspecting them closely. I noticed that the plastic float has an aluminum tab that the needle hooks on to. This piece of aluminum is loose. Basically when the fuel in the bowl is going down it lifts up on a needle and lets fuel in. With this being loose it doesn't open up far enough to let enough fuel in.

COULD THIS BE THE PROBLEM?

Is there a way to tighten this tab down? Its hard to explain, but this alum tab has plastic melted to hold it in place. I'm thinking that using a soldering iron to melt it down more should do the trick. Do you think it will blow up because it has been living in fuel for 20 something years?

Probably not, but I'd wear a face shield and safety glasses anyway.

Any fuel pressure at all will blow the needle out of the way if the float isn't pressing on it. More likely it's flooding when it's failing.

 

[duhn]

Re: '86 blackmax 150 hp: Loss of Power

Update....
I rebuilt the carbs with different floats. It still has the same problem. This time it took 32 miles for it to act up.

The only things I haven't changed up are the stator, trigger and switch boxes. Do any of these act this way when they are going bad? or are they like a switch, either they work or don't, no in-betweens?

Does compression change with the motor temp?

 

[duhn]

Re: '86 blackmax 150 hp: Loss of Power

Just checking all avenues. The green wire that comes from the oil injection warning module goes to the switch box. Besides a warning buzzer, does this green wire send a signal to the switch box to shut the motor down?

 

[sschefer]

Re: '86 blackmax 150 hp: Loss of Power

J_Martin can probably answer that question best. I took the advance module and the alarm module off mine when I removed the the oil injection. There is a green wire that goes to the switch box but I think it just gets voltage as a signal and that along with the the oil pump rotational sensor tells the module that the engine is running and the oil pump is rotating.

Your engine may have an advance module that ties into the switchbox Bias circuit and if it's faulty and failing because of heat then it might cause the problem. Seems the defacto standard recommendation is to remove the advance module from these engines. It is no longer available from Merc parts so I suspect that Merc agrees, (just a suspicion). Max advance timing changes are usually necessary to regain peak performance when you do this. I left mine at 19 because it is still in break-in but will probably take it slowly up to 22 later.

I think you can safely disconnect it on your engine and test since the Merc tune up procedures require that it be disconnected when setting the timing. It ties into the switch box at the White/black stripe wire (bias) that electrically connects the two switchboxes together. Peak performance may suffer some but in general it would be stable and not dramatic like yours seems to be.

Just out of curiosity, does this engine ever sound like it might be rattling when this problem occurs. I ask this because I had a coil that was bad on a 4 cylinder that would run great for about 15-20 mins then start loosing power and rattle. The coil would get warm and begain collapsing (firing) early then quickly fire a second time (double fire). I chased the problem for months and threw money at it left and right only to find it was a 30.00 part.

I suggest that at this point you run it somewhere that you have shore power and use a hair dryer (not a heat gun) to warm up the various electrical components and try to reproduce the problem. The change in the way the engine runs may be subtle so if you think you've found something, let it cool and see if you can reproduce it. If you can you've might have found the problem.

These are just some ideas from my own experiences. I hope they help you find your problem.

Steve

 

[duhn]

Re: '86 blackmax 150 hp: Loss of Power

I almost gave up and took it to a local mechanic. I was talking to the guy and explained the situation. First thing out of his mouth was, sounds like stator or switchboxes breaking down and failing from the heat. He was going to charge $170 to dyno it. I figured I could spend that money on a new stator and switchbox. Thats where I am at now.

John, Steve,
thanks for chiming in on my other post about the stator and voltage regulator. After this, the entire electrical ignition system has been replaced.

 

[duhn]

Re: '86 blackmax 150 hp: Loss of Power

Close this thread....Problem solved!!!!
Man, it took a while to get everything straightened out. I had an issue with an on-line purchase, had an episode with one of the carbs leaking from a stuck float, Holidays etc.etc.

During this down time I also fixed the tach and replaced the prop. People have told me that I should switch out the 4 blades to a 3 blade. Did that today and took it for a test run. We have a new top speed record of 37.5 knots at 5100 rpm at WOT. This is with a 21 pitch and I do plan on getting a 19 pitch. With the 3 blade prop, the motor did'nt bog down going up the back side of a swell.

Here is a list of what was done to fix this problem: new stator, trigger, switch boxes, plug wires and coils.

I hate that i love my boat so much. Repairing this boat has become an obcession, and I couldnt have done it without you guys, thanks.

 

[hkeiner]

Re: '86 blackmax 150 hp: Loss of Power

My latest issue has been the motor would occasionally lose power after a long outing, 20 to 30 miles. I would have to throttle down to avoid stalling. Then it would get back on plane, then do it again. It seems like going up the backside of a swell causes this. As the day progresses it will not go faster than 5 knots.

For my own education on troubleshooting, are you saying that the symptoms you described in your first post (as quoted above) went away after changing from a 4-blade prop to a 3-blade prop or was it from replacing all of the other parts you mention? I would never have guessed that changing the prop would be a solution.

 

[duhn]

Re: '86 blackmax 150 hp: Loss of Power

For my own education on troubleshooting, are you saying that the symptoms you described in your first post (as quoted above) went away after changing from a 4-blade prop to a 3-blade prop or was it from replacing all of the other parts you mention? I would never have guessed that changing the prop would be a solution.

Replacing the all the ignition parts fixed the loss of power. The 3 blade prop enables the boat to go up hill with out bogging down.